Low-noise millimeter-wave synthesis from a dual-wavelength fiber Brillouin cavity

In this Letter, a photonic system is proposed to generate millimeter waves with low phase noise and ultra-high frequency stability. By locking two free-running CW lasers to the same fiber cavity whose free-spectral range is actively stabilized, millimeter waves can be synthesized in a wide frequency range with fine-tuning capability. Exploiting the spectral narrowing effect of stimulated Brillouin scattering, the generated millimeter waves exhibit low phase noise that does not scale up as the frequency increases. In the experimental demonstration, up to ∼300  GHz millimeter waves are generated, with a phase noise of <-90  dBc/Hz at 10 kHz offset limited by the local oscillator and an in-loop 60 min frequency RMS drift of 0.43 mHz. The output frequency of the system can be readily increased to sub-THz region by replacing one of the pump CW lasers.